If you need to use the entire carton of broth and want to be able to pour it quickly without a lot of glugging and splashing, then un-stick the folded corner on the side opposite the pour spout. Fold that up, and trim the corner. Push the sides to make sure that it opens, and pour away!
This allows air to come in somewhere other than the pour spout, so you don't get the glugs and splashes. Yay!